Method of drying materials with superheated steam.



Patented Apr 13, 1909.

D. B. LAIN. METHOD OF DRYING MATERIALS WITH SUPERHEATED STEAM. APPLIOATION FILED NOV. 16,1908.

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DAVID E. LAIN, OF BELLINGHAM, WASHINGTON, ASSIGNOR OF ONE-HALF TO EDWIN G. JEWETT, OF BELLINGHAM, WASHINGTON.

METHOD OF DRYING MATERIALS WITH SUPERHEATED STEAM.

Specification of Letters Patent.

Patented April 13, 1909.

Application filed November 16, 1908. Serial No. 462,920.

T 0 all whom it may concern:

Be it known that I, DAVID E. LAIN, acitizen of the United States, and a resident of Bellingham, in the county of Whatcom and State of Washington, have invented certain new and useful Improvements in Methods of Drying Materials with superheated Steam, of which the following is a specification.

This invention has relation to the art of drying substances or materials in general which will not be injured by a temperature somewhat above 212' Fahrenheit; but it relates more (particularly to the art of drying lumber, an the apparatus and process described have been designed with a special reference to that use. In this art it has been common to use heated air for the dr ing medium. Although this method is s ow, expensive, dangerous, as to combustion, and with pitchy woods, unsatisfactory, it is used almost exclusively at the present time. Recently a method of drying lumber with superheated steam has come into a limited use. This medium drys lumber rapidly, with little or no checking, with no danger from combustion and by it the turpentine is absorbed from pitchy woods and the resinous matter permanently fixed in the pores of the same. At present, by this method superheated steam is passed in the bottom of the drying chamber and escapes from the top of the same either directly into the outer air, or it is first carried through flues in the hollow walls of the drying chamber. But no means are employed to indicate when the drying rocessis completed. By this direct metho of using the su erheated steam there is great loss of energy ue to the energy contained in the exhaust steam. Also, because of the great amount of heat energy contained in the exhaust, it is impracticable to condense the same in order to save the turpentine when pitchy lumber is being dried.

My method is an improvement on the direct method of drying with su erheated filling the drying chamber and conduit connections with steam to the exclusion of air, forcing a circulation of said steam in a continuous flow through a closed circuit including the drying chamber and a steam superheater, ausin' a temperature and gravit separation 0 the steam while passing t rougha part of said circuit in order that the surplus vapor, due to the evaporation of moisture from the material being dried, may be selected from the coolest and heaviest of the circulating vapor, causing this selected surplusage to be ejected from said circuit without interru ting the continuous flow of the steam in t e same, when desired, causing said surplus vapor to pass through a steam condenser and the liquid condensed therefrom into a settling tank, taking the temperature of the steam in said circuit on both sides of the material being dried in order that the rate of the work being done on the same may indicate the time when the process should cease and finally, when desired, reducing the temperature in the dryin chamber by introducing cooler steam beibre the same is o ened to withdraw said material.

The ob ect of my invention is to dry lumber with ess checking, in less time, with less risk of combustion, with more complete removal of volatile oils, with more complete fixing of resinous matter and with less expense than is possible by heated air; and with less expense, with more certainty of results and in a manner that will permit of greater saving of valuable by-products than is possible with the methods at present employed to dry lumber by superheated steam. 'lhe ap aratus that I use to accomplish these resu ts is described in my application for a (patent for an improvement in superheate steam dry-kilns, filed July 6, 1908, Serial Nuinper 442,197. In the latter part of the specification forming a part of said application I make the following statempntz- The descending hot steam on reaching the pile of lumber is-cooled thereby, and is conse uently drawn down through the same. Therefore, good results can be obtained by having the kiln se arated into upper and lower rooms by a oor on the track level, having this floor tight, except for openings on one side-"this floor can with advantage be inclined downward toward the side having the openings then having 'the c0nstruction below this floor similar to that already describcd as being used below the diaphragm 36. That is, the floor of the upper room ma serve in place of diaphragm 36 and the true floors and casings be dis ensed with. This simplification is especia y desirable where a number of trucks containing lumber are in one compartment.

Any suitable apparatus may be used in carrying out my rocess. The apparatus that I illustrate an describe in this application embodies the simplification referred to in the above extract, and is here illustrated in one sheet of drawingsin which similar l I Fig. 2 is an end elevation of the dry-kiln sectionalized on a transverse plane through line a b, Fig. 1.

More specifically, 2, 2 etc. are the inclosing walls of a dry-kiln consisting of the drying chamber 1 and the separator'compartment 35. These two rooms are separated by a diaphragm 36 which is declined toward that end where there is an opening forming a connection between the two rooms. Immediately above this diaphragm are the I beams -9, 9,. etc. arranged in a horizontal plane, resting on ledges in the side walls and furnishing suitable supports for the tracks 8, 8, 8. On said tracks are the lumber trucks consisting of frames 6, 6, etc. on wheels7, 7, etc. On these trucks are stacked the piles of lumber- 3, 3, 3, shown only in outline. The separate pieces of lumber constituting these piles are arranged in the well known open manner which permits the access of the drying medium to the major portion of all surface of the same. The tracks 8, 8, 8, ass from the mill yard into one end of the kiln and out at the other, there being an opening at each end of the kiln closed by the vertically-sliding doors 12, 12. These doors are supported on ropes 14,14, etc., passing over sheaves 15, 15, etc. supported in bearings on posts 17, 17, etc. a section of each of which 1s removed in order to secure a tight closure, these doors are clamped to the kiln by top, screw clamps 24, 24, etc. side, screw clamps 26, 26, etc. and

. bottom wedges 58, 58, etc.

baflie plates 60, 60, 60. Transversely across one end of the separator compartment 35 and beneath'the closed end of diaphragm 36 is the perforated pipe 40, this pipe connects Q with pipe 41 on the exterior. Below this perforated pipe is the short, declined diahragm 37. Below diaphragm 37, leading rom the lowest part of the separator compartment 35, is exhaust pipe 39. This has two branches one an outlet into the outer air through valve 39, the other entering the manifold 53 of a steam condenser through pipe 39". Said manifold is located'in water tank 54 supplied with cold water through inlet pipe 55 and overflows through pipe 56.

. The manifold 53 empties through pipe 53 into settling tank 57. Said tank has a standpipe outlet 57 The steam-superheater manifolds 50, 50, etc. are inclosed in furnace walls 75, having a stack 79, grate bars 76, fire-box roof 80, a direct opening into stack through flue 77 c1os-. able by damper 77, 77, and an indirect opening into stack through fine 78 closable by damper 7 8, 78". The cooler side of manifold 50 is entered through header 45 and the hotter side is emptied through header 46. Pipe 46 leads from the header 46 into the top of kiln I. Pipe 41 leads from perforated pipe 40 through blower or fan 42 into pipe 45, which in turn leads into header 45. Blower 42 is driven by belt 42 from a source of power not shown. Ther mometer 51 is inserted in pipe 46 and thermometer 52 is inserted in pipe 41. Pipe 49 leads from a boiler, or other source of steam not shown-into pipe 46 through two branches in which are located valves 49 and 49". In pipe 46 between the points where said branches enter is valve 46".

To operate this dry-kiln: The lumber is loaded on the trucks in open order, as eX- plained, the piles 3, 3, 3, thus formed are run into the kiln 1, the doors 12, 12, closed and clamped as described. The valve 39 in pipe 39 is opened, valve 46 in pipe 46 is closed, valve 49 is closed, valve 49" inpipe 49 is opened and steam is permitted to enter the top of kiln 1 through pipes 46. hen the kiln is completely filled and all the air expelled therefrom steam will pass freely from exhaust pipe 39. Then valve 49 in pipe 49 is opened and the air in the superheater pipes and connections is driven into the separator compartment 35 through perforated pipe 40. When the steam again flows freely from exhaust pipe 39, the whole system'is completely filled with steam and the air, expelled. Now valves 49 and 49? are closed, thus shutting off the source of steam, valve 46 opened, damper 77, 77" is closed, (it is assumed'that there is a fire burning on grate 76) damper 78, 78" is opened and blower 42' is caused to revolve in a direction which will force the steam into header 45 through manifolds 50, where it is superheated, into header 46 through pipe 46 into .the top of kiln 1 through the three branches of pipe 46, where it comes into contact with the cool piles of lumber 3,3, 3, is cooled thereby and thus drawn to them and percolates down through the same, reaches the upper side of diaphragm 36, passes along the'same and around its lower end where it passed through the superheater manifolds 50 as before. Thus a continuous circulation of the steam is established and maintained, by means of blower 42, through the circuit consisting of drying chamber, separator compartment and superheater manifolds as described. After this circulation has been maintained for a time, the steam will absorb moisture from the lumber which will add to the volume of steam to an extent beyond the carryingcapacity of said circuit at the rate of flow maintained by the blower. Then the cooler and heavier parts of the vapor as it passes through separator compartment 35 will be crowded down to the deeper part of the same and expelled through exhaust outlet 39. In the event that lumber is being dried which contains no valuable by-product, the exhaust is permitted to pass directly into the outer air through open valve 39. But if the wood being dried contains turpentine bearing pitch, then valve 39 is closed,

the exhaust va ors are passed through condenser manifol 53and the liquid condensed therefrom passes out of pipe 53 into settling tank 57, Where the turpentine rises to the top and can be readily removed, while the water passes. out from the bottom through standpipe outlet 57'.

The walls of the kiln are constructed in a manner to resist the passage of heat, and the exposed steam pipes and blower are covered with non-heating-conducting material, not shown. Hence the loss of temperature from these sources will be quite constant for a given initial temperature of the steam. Knowing the amount of this loss in degrees, the difference in temperature recorded by thermometers 51 and 52 will at any time be an indication of the rate of evaporation of the moisture from the lumber. When this rate materially diminishes, under constant initial temperature as indicated by thermometer 51, the moisture is nearly all extracted from the lumber and the operation can be stopped before the lumber has been over-dried.

When it is considered desirable to reduce the temperature of the kiln before opening the same for the removal of the lumber, boiler steam, or exhaust steam from an engine, can be introduced into the kiln as described. Otherwise, this closing step in the process as described can be omitted.

Having thus fully described the method and process by whichl attain the objects of my invention, I claim,

1. The method of drying lumber or other moisture bearing material consisting in forc ing live steam to fill an endless circuit including said material, cutting off the supply of live steam, enforcing in said circuit circulation of the confined steam and the vapor emitted from the drying material, superheating this mixed medium while circulating, and separating the excess moisture therefrom by gravity during such circulation.

2. The method of drying lumber or other moisture bearing material, consisting in forcing live steam to fill an endless circuit including said material; cutting ofl the supply of live steam, enforcing in said circuit circulation of the confined steam and the vapor emitted from the drying material, su erheating this mixed medium while circu ating, separating the heavier va ors therefrom without application of coo 'ng means other than the drying material itself, expelling said heavier vapors from the cir cuit, and continuing this process until no more vapor is emitted from the drying material 3. The method of drying lumber or other moisture bearing material, consisting in forcing live steam to fill an endless circuit including said material, cutting off the supply of live steam, enforcing in said circuit circulation of the confined steam and the vapor emitted from the drying material, superheating this mixed medium while circulating, separating the excess moisture therefrom by gravity during such circulation, and then admitting fresh steam into the circuit to cool the material before removing the same. 4. The method of drying lumber, or-other moisture-bearing material, consisting in causing the steam to occupy the space around said material and to fill an endless circuit including the same, causing steam to traverse said circuit, superheating it while it is circulating, separating and ejecting the surplus vapor and moisture from said clrcult without interrupting said circulation, and continuing said circulation and resuperheating of the steam until the temperature difference between the steam, as it enters said space around said material and as it leaves the same, indicates that said material has been brought to the desired state of dryness. Signed at Bellingham in the county of Whatcom and State of Washington this tenth day of November A. D. 1908.

DAVID E. LAIN. 

